This invention relates to the field of liquid crystal polymer ("LCP") blends, particularly thermoset blends that include an epoxy-functional rubber compound.
Thermoset compositions characteristically cross-link and become hard, or "set", when cured for a sufficient period of time. This change is permanent. Consequently, a molded part made of thermoset resin cannot be reworked. Often it is difficult to produce complex shapes with thermoset plastics because the cross-linking reaction hardens the material before molding can be completed. Advantageously, cured thermoset plastics tend to exhibit good thermal and chemical resistance.
Thermoplastic compositions will flow when heated above their glass transition temperature, or melt transition temperature (if present), and solidify upon cooling, but these changes are reversible. They can be molded into complex shapes and worked into almost any form, e.g. film, fiber, and so forth. The form may not be permanent, however; if the thermoplastic article is heated above its glass or melt transition temperature the plastic will become soft and begin to flow, destroying the shape of the material.
Liquid crystal polymers are generally thermoplastic. They characteristically exhibit a high degree of anisotropy, stiffness and chemical resistance, and can be used to make a wide variety of products.
Epoxy resins generally fall into the category of thermoset compositions, since the highly reactive epoxy moiety tends to undergo irreversible cross-linking reactions. Rubber compounds often do not thermoset, however; these compounds also lack the physical strength and chemical resistance of LCP compounds. Where a rubber compound contains epoxy functional groups, the percentage of epoxy groups in the compound will affect the thermosettability thereof. If a large, bulky rubber compound contains a relatively small number of epoxy groups, it may not thermoset.
U.S. Pat. No. 4,710,547 describes a process for producing a three-dimensionally cross-linked polyester having a liquid crystal structure wherein a thermotropic liquid crystal polyester is combined with a multifunctional species that cross-links the LCP to immobilize the liquid crystal structure.
U.S. Pat. No. 4,842,924 discloses a process for fabricating a composite material made by forming a network of microfibrils made from a rigid-chain polymer, and then interpenetrating the network with two continuous phases, one matrix-forming and the other reinforcing. The rigid-chain polymer may have liquid crystalline properties, while the matrix phase may be a thermostat resin such as an epoxy resin.
U.S. Pat. No. 4,764,581 discloses liquid crystalline diglyceridyl compounds of optionally ring-substituted 4-hydroxyphenyl 4-hydroxybenzoates, and epoxy resin mixtures containing those compounds.